a）相关定义：
- Software Fault : A static defect in the software
- Software Failure : External, incorrect behavior with respect to the requirements or other description of the expected behavior
- Software Error : An incorrect internal state that is the manifestation of some fault
b）题目描述：
c）相关问题及作答：
n Identify the fault.
Answer：左边的程序代码for循环不能到达x数组下标为0的位置，产生了数据遗漏；右边程序代码实现的功能是找出x数组中第一个0出现的位置，而不是最后一个0，程序功能和描述不符。
n If possible, identify a test case that does not execute the fault. (Reachability)
Answer：左边程序：x = null, y=0；右边程序：x = null。
n If possible, identify a test case that executes the fault, but does not result in an error state.
Answer：左边程序：x = [5,2,0], y=5；右边程序：x = [3,6,9]。
n If possible identify a test case that results in an error, but not a failure.
Answer：左边程序：x = [5,2,0], y=8；右边程序：x = [5,0,2]。
